The present disclosure relates generally to the field of automated maintenance (including non-destructive inspection) of aircraft structural elements, and more particularly to an automated end effector-carrying apparatus that is coupled to and travels along an integrally stiffened wing box while performing a maintenance function. As used herein, the term “maintenance” includes, but is not limited to, operations such as non-destructive inspection (NDI), visual inspection, drilling, scarfing, grinding (e.g., to remove bonded or bolted components), fastening, appliqué application, ply mapping, depainting, cleaning and painting.
A variety of elongated composite structures may have relatively confined internal cavities that require inspection in order to assure that the structure meets production and/or performance specifications. One known elongated composite structure with tapering internal cavities is an integrally stiffened wing box for an airplane. One example application is in the horizontal stabilizer of an aircraft. A horizontal stabilizer structural box may be fabricated as a large co-cured structure that requires the use of soft internal tools to facilitate tool removal after the cure. If a given co-cured composite structure is considered primary structure, it would therefore need to be inspected to ensure structural integrity.
One of the requirements for certification of a composite-based airplane horizontal stabilizer is to perform a complete set of NDI scan of all the composite structural elements. Methods for scanning the interior surfaces of a horizontal stabilizer using a modular, magnetically coupled transporter system have been disclosed, for example, in U.S. patent application Ser. No. 13/534,014. With regard to the exterior surfaces of a horizontal stabilizer, it is known to use a large gantry mechanism that moves an ultrasonic maintenance tool over a surface skin. This gantry-based system is expensive, requires extensive training to operate, and occupies a large space, which limits the flexibility in setting up NDI work cells for scanning of horizontal stabilizers It also requires that the horizontal stabilizer be turned over to scan the opposite surface.
It would be desirable if a process were available that could scan wing box surface skins without the need for a gantry-based mechanism for movement of the NDI sensor array. An additional benefit would be if the surface skin scanning process were compatible with the aforementioned process for scanning the interior surfaces. Accordingly, there is a need for a system for inspecting the exterior of a wing box and similar elongated hollow structures that can provide such benefits.